Drop building on i686-linux

Dependencies

• [2] IZYR3KTL release.nix: Get rid of the "system" argument
• [3] T4LLYESZ * Nix expression for building Hydra.
• [4] LOHWNXEJ Cleanup

Change contents

• replacement in release.nix at line 9
  [2.37]→[2.37:102](∅→∅)
  − genAttrs' = pkgs.lib.genAttrs [ "x86_64-linux" "i686-linux" ];
  [2.37]

  [3.0]
  + genAttrs' = pkgs.lib.genAttrs [ "x86_64-linux" ];